The present invention relates to a surveying instrument, by which it is possible to perform a surveying operation automatically on true north.
In a case where a surveying instrument is installed for the purpose of performing a surveying operation, the true north is measured for setting a sighting direction of the surveying instrument. As one of the methods to determine azimuth at a position of installation, a method is known, by which the true north is surveyed by utilizing the sun.
When a position (latitude and longitude) where the surveying instrument is installed is already known, a sighting is performed from the position of installation toward the sun by using a telescope. A directional angle of the sun when the sighting is performed is obtained, and the true north can be surveyed based on the directional angle and time moment when sighting is performed.
It is dangerous to sight the sun directly. And when sighting is performed based on an image of an image pickup element acquired through a telescope, a big burden is imposed on the image pickup element. For this reason, normally, sighting is performed on the sun by mounting a filter on the telescope and attenuating the light by means of the filter.
In a normal surveying operation of the surveying instrument, a filter for light attenuation is not necessary and the filter is mounted for performing a true north surveying. Therefore, to perform the true north surveying, there have been problems in that a filter for light attenuation must be prepared and the filter for light attenuation must be mounted on the surveying instrument without forgetting.